Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

The government said it will start considering proposals to sell genetically engineered animals as food, a move that could lead to faster-growing fish, cattle that can resist mad cow disease or perhaps heart-healthier eggs laid by a new breed of chickens.

The rules will also apply to drugs and other medical materials from genetically engineered animals, a field with explosive potential.

U.S. supermarkets currently sell no meat from genetically engineered animals. But a Boston-area company called Aqua Bounty Technologies hopes to win approval next year for its faster-growing salmon and make the fish available by 2011. "It tastes just like any other farm-raised salmon," said vice chairman Elliot Entis, who has sampled it.

Reaction from consumer groups was mixed. They welcomed the government's decision to regulate genetically altered animals, but they cautioned that crucial details remain to be spelled out. For example, the Food and Drug Administration does not plan to require that all genetically engineered meat, poultry and fish be labeled as such. It would be labeled only if there was a change in the final product, such as low-cholesterol filet mignon.

"They are talking about pigs that are going to have mouse genes in them, and this is not going to be labeled?" said Jean Halloran, director of food policy for Consumers Union. "We are close to speechless on this." Consumers Union publishes Consumer Reports magazine.

Nonetheless, Gregory Jaffe, who heads the biotechnology project at the Center for Science in the Public Interest called the FDA's move a "good first step."

"This is the first time the federal government is announcing a comprehensive regulatory system that addresses the concerns from these animals," said Jaffe. "But it may not have addressed all the environmental concerns."

What would happen if a genetically engineered animal escaped and started reproducing with wild animals of the same species? asked Jaffe. The FDA said it would address that issue.

On Thursday, the FDA released a proposed legal framework for how it would resolve such questions as whether the altered animals are safe for human consumption and whether they pose any serious environmental risk. FDA officials said they were focusing on animals that will be used as food, or to produce medications that would then be consumed by people or by other animals. The agency is not interested in reviewing genetically engineered mice already widely used in lab experiments.

"Genetic engineering of animals is here and has been here for some time, " said Larisa Rudenko, a science policy adviser with the FDA's veterinary medicine center. "We intend to provide a rigorous, risk-based regulatory path for developers to follow to help ensure public health and the health of animals."

Genetic engineering is already widely used in agriculture to produce higher-yielding or disease-resistant crops. But it's unclear how consumers will react to altered animals, even if they come with a government seal of approval.

Genetically engineered — or GE — animals are not clones, which the FDA has already said are safe to eat. While clones are exact copies of an animal, genetically engineered animals are manipulated by scientists to bring about a change in their characteristics. In years past, this was done by crossbreeding animals with desirable traits.

GE animals are created when scientists insert a gene from one species of animal into the DNA of another animal to reprogram some of its characteristics. For example, fish could be made to grow faster, or pigs might be re-engineered to produce less waste.

To engineer Aqua Bounty's faster-growing salmon, scientists took a snippet of DNA from an eel-like fish and stitched it into the genes of salmon. Normally, Atlantic salmon produce growth hormone only in the summer months. But with the change, salmon produce growth hormone all year long, allowing them to grow to full size in about 18 months instead of three years, Entis said.

"This is like tuning up your car," he said. GE salmon would be kept in enclosed pens, to prevent their escape into the wild, and sterilized to keep them from reproducing.

While the introduction of GE animals by food companies will probably get the most attention from the public, it's the pharmaceutical industry that seems poised to reap the greatest benefits.

Barbara Glenn, an animal science expert with the Biotechnology Industry Association, said research is under way that could lead to the development of vaccines, transplant organs, replacement tissues, and other medically useful materials from genetically engineered animals.

For example, one company is experimenting with GE cows to produce human antibodies against such diseases as smallpox and pandemic flu. Another is trying to produce a pig liver that would be suitable for transplanting into a human patient.

Glenn said there is currently only one drug on the market derived from a genetically engineered animal, and it is not approved in the U.S. Available in Europe, the medication is an anti-blood clotting factor produced from the milk of GE goats.

"We are issuing this draft guidance now because the technology has evolved to a point where the commercialization of these animals is no longer beyond the horizon," said Randall Lutter, FDA deputy commissioner for policy. The agency's proposal will be open for public comment for 60 days.

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